1. Field of the Invention
The present invention relates to vehicle sensors and, more specifically, to a vehicle sensor that determines the presence and weight of a seat occupant.
2. Description of the Prior Art
The performance of an automotive air bag system, in terms of its success or failure in preventing serious personal injury, may depend upon the size of the passenger present in the vehicle. For example, if the passenger is of relatively small size such as a child, the passenger may be seriously injured by the deployment of the air bag at full force. In another example a passenger may not be present in the passenger side seat of a vehicle and in the event of an accident, a deployment of the airbag results in an unnecessary cost of repair. Therefore, it is desirable to measure the weight in the seat of an automobile to determine whether, in a crash, to deploy the airbag at full force, partial force, or simply not at all.
Various hardware configurations have been employed to measure the weight of a vehicle passenger. One existing solution uses a number of load sensors distributed beneath the seating surface of the vehicle seat. The load sensors measure the compressive load generated by the weight of the seat occupant. One deficiency of this approach is that each load sensor can only measure the compressive load at one localized point on the seat surface. Since the position of an occupant upon the seat may vary with the size and physical attributes of the individual, several load sensors would be required about the base of the seat and, in some cases, also in the seat back rest. An electronic processing unit is required to interpret the multiple sensor data and make an estimation of passenger size. Such systems are cost prohibitive due to the high initial cost of the multiple load sensors and the electronics required. In operation, the multiple sensors systems are difficult to calibrate and the accuracy of the system over time is suspect.
Another solution uses a load cell at each of the four mounting points of the seat. The measurements from the four sensors are combined to find vehicle occupant weight. This system suffers from the difficulty of precisely matching the mounting planes of the seat and its base. Any mismatch in the seat mounting planes results in an error in the total weight measurement of the vehicle occupant. Additionally, the system cost is high due to the need for multiple load cells of high precision, wiring and connectors for each load cell, and multiple sensing amplifiers.
Therefore, it would be advantageous to provide a system that allows for the cost effective measurement of the weight of an automotive seat occupant. Such a system should provide for the accurate measurement of an occupants weight over the operating life of the vehicle. It is to the provision of such an improved system that the present invention is primarily directed.